Information Gain calculation query

[Ubik]

Greetings, I wondering if I have misconstrued or missed a step in the calculating the information gain shown in the last two lines of this slide. I was able to calculate the Entropy with formula provided on a previous slide but am unable to get the same answer for these 3 equations(answers from left to right - = 0.28, =0.03, =0.12). I must missing something.

For example: The first equation 0.5 - (0.5*(0.8) + 0.5*(0.2)). My answer is 0. The answer shown is 0.28.

Apologies, can someone illuminate. Thank you very much.

m

[SamReiswig]

Hi Ubik!

Following the slides we have
H(0.5) = 1
H(0.8) = H(0.2) = 0.72
And the calculation:
H(0.5) - (5/10 * H(0.8) + 5/10 * H(0.2))
Which becomes:
1 - (0.5 * 0.72 + 0.5 * 0.72)
1 - (0.36 - 0.36)
1 - 0.72
0.28

Hope this helps!

[Ubik]

Thank you so much for your swift-calculation-clarity Sam! I will return to the video and review the process with this in mind. Let the confusion dispelling begin! Thank you for your time and expertise.

Ubik